Hickenlooper, who stood in the West foyer of the state Capitol and was surrounded by lawmakers and law enforcers, said the state’s previous home-grow limits of 99 plants for medical marijuana purposes effectively created “large-scale grow operations in people’s homes.”

“So by setting a limit of 12 plants per home, I think we’re protecting neighborhoods from violence often associated with illegal drug trafficking,” he said during the public bill-signing ceremony.

The 12-plant cap puts Colorado more in line with other states that have marijuana programs in place, and it also could hit at the heart of gray market activity, Hickenlooper said following the ceremony.

“But we know for a fact that people are pretending to grow medical marijuana and then exporting it to other states — not one, not two, many,” Hickenlooper told The Cannabist. “So we’re trying to tighten that loophole up.”

Colorado’s Amendment 64 approved by voters in 2012 allows an adult age 21 and older to cultivate up to six marijuana plants, with a maximum of three in a mature, flowering state. A number of municipalities, including Denver, already have set caps on the number of plants allowed in a residence, regardless of how many adults live there.

HB 1220 was amended to allow for medical marijuana primary caregivers with “exceptional circumstances” to have up to 24 plants, if they register with the state.

Alicia Wallace is a business reporter who specializes in covering the cannabis industry for The Denver Post and, formerly, for its web vertical The Cannabist. In her 15 years as a business news reporter, her coverage has spanned topics such as the...